1. Field of the Invention
This invention relates to a base tube for a fuel cell, whose porosity and pore diameter are increased to improve the power generation characteristics of the resulting fuel cell, and a material for the base tube.
2. Description of the Related Art
FIG. 1 shows the outline of a base tube of a thermal spray type solid electrolyte fuel cell.
As shown in FIG. 1, a thermal spray type solid electrolyte fuel cell (SOFC) is produced in the following manner: A cermet of Ni and yttria-stabilized zirconia (YSZ) is provided in a film form by plasma spraying on a porous cylindrical base tube 1 of calcia-stabilized zirconia (CSZ) to serve as a fuel electrode 2. On this fuel electrode 2, oxygen ion-conductive YSZ is provided in a film form by plasma spraying to serve as an electrolyte 3. On this electrolyte 3, LaCoO3 is provided in a film form by acetylene flame spraying to serve as an air electrode 4. In this manner, a fuel cell is constructed. Finally, the fuel electrode 2 and the air electrode 4 are connected together in series by an electrically conductive connecting material (interconnector) 5 in a film form composed of a cermet of NiAl and alumina.
The production of a fuel cell by thermal spraying as an earlier technology is laborious and costly, and should be decreased in cost. Thus, a co-sinter type fuel cell, which is composed of a base tube, a fuel electrode and an electrolyte sintered integrally, and which requires a reduced number of sintering operations, has been developed. However, this type of fuel cell poses the problem of insufficient gas permeability of the base tube for achieving desired power generation characteristics.
Another problem with the base tube of the earlier technology is marked deterioration, at a rapid temperature raising and lowering rate during a heat cycle. In detail, with a temperature raising and lowering rate of not higher than 50xc2x0 C./hour, the performance of the cell after the heat cycle does not differ from its performance before the heat cycle. At a temperature raising and lowering rate in excess of 50xc2x0 C./hour, on the other hand, an output drop of about 10% may occur per heat cycle. When fuel cells are used as a gathering, a temperature raising and lowering rate, if not made very slow, exceeds 50xc2x0 C./hour in a part of the fuel cell gathering, thereby damaging the cell. Thus, there is a demand for a cell which is not damaged even at a rapid temperature raising and lowering rate of about 200xc2x0 C./hour.
Another challenge for the base tube is to improve the fuel utilization factor. The fuel utilization factor of the base tube according to the earlier technology is about 70% of fuel charged. An improvement achieved in the fuel utilization factor can lead to an increase in the efficiency of the fuel cell.
In light of the above-described circumstances, the present invention aims to provide a base tube for an integral sinter type fuel cell, the base tube having increased porosity and pore diameter to improve the power generation characteristics of the fuel cell, and the base tube being free from damage at a rapid temperature raising and lowering rate, and having a higher fuel utilization factor; and a material for the base tube.
A first aspect of the invention is a base tube for a fuel cell, the base tube comprising a mixture of a raw material for the base tube, and coarse particles, whereby the mixture shrinks nonuniformly when sintered to increase the porosity of the base tube. Thus, the gas permeability performance can be improved, and the electrical efficiency of the cell can be increased.
A second aspect of the invention is the base tube for a fuel cell according to the first aspect of the invention, wherein the mean particle diameter of the raw material for the base tube is 0.5 to 2 xcexcm, and the particle diameters of the coarse particles are 5 xcexcm or more. Thus, the porosity can be increased.
A third aspect of the invention is the base tube for a fuel cell according to the first or second aspect of the invention, wherein the mixture contains 10 to 40% by weight of the coarse particles. Thus, the porosity can be increased.
A fourth aspect of the invention is the base tube for a fuel cell according to the first to third aspects of the invention, wherein the raw material for the base tube is calcia-stabilized zirconia (CSZ). Thus, the porosity can be increased to 20% compared with the conventional value of 15%, so that the electrical efficiency of the cell can be increased.
A fifth aspect of the invention is a base tube for a fuel cell, wherein a raw material for the base tube is fine particles of calcia-stabilized zirconia (CSZ), and fine particles having the same particle diameter as the particle diameter of the raw material are mixed with the raw material, the fine particles being selected from one or more of NiO, CoO, FeO, Fe2O3, CaTiO3, SrTiO3, and BaTiO3, whereby a mixture of the fine particles and the raw material shrinks nonuniformly when sintered to increase the porosity of the base tube. Thus, the electrical efficiency of the cell can be increased.
A sixth aspect of the invention is the base tube for a fuel cell according to the fifth aspect of the invention, wherein the mean particle diameter of the raw material for the base tube is 0.5 to 2 xcexcm. Thus, the electrical efficiency of the cell can be increased.
A seventh aspect of the invention is the base tube for a fuel cell according to the fifth or sixth aspect of the invention, wherein the mixture contains 10 to 40% by weight of the fine particles.
An eighth aspect of the invention is a base tube for a fuel cell, wherein a raw material for the base tube is calcia-stabilized zirconia (CSZ) having a mean particle diameter of 0.5 to 2 xcexcm, and coarse particles having particle diameters of 5 xcexcm or more are mixed with the raw material, the coarse particles being selected from one or more of NiO, CoO, FeO, Fe2O3, CaTiO3, SrTiO3, and BaTiO3, whereby a mixture of the coarse particles and the raw material shrinks nonuniformly when sintered to increase the porosity of the base tube. Thus, the electrical efficiency of the cell can be increased.
A ninth aspect of the invention is the base tube for a fuel cell according to the eighth aspect of the invention, wherein the mixture contains 10 to 40% by weight of the coarse particles. Thus, the electrical efficiency of the cell can be increased.
A tenth aspect of the invention is a base tube for a fuel cell, wherein a raw material for the base tube is calcia-stabilized zirconia (CSZ) having a mean particle diameter of 0.5 to 2 xcexcm, and fine particles having particle diameters of 0.5 to 3 xcexcm, and coarse particles having particle diameters of 5 xcexcm or more are mixed with the raw material, the fine particles being selected from one or more of NiO, CoO, FeO, Fe2O3, CaTiO3, SrTiO3, and BaTiO3, and the coarse particles being selected from one or more of NiO, CoO, FeO, Fe2O3, CaTiO3, SrTiO3, and BaTiO3, whereby a mixture of the fine particles, the coarse particles and the raw material shrinks nonuniformly when sintered to increase the porosity of the base tube. Thus, the electrical efficiency of the cell can be increased.
An eleventh aspect of the invention is the base tube for a fuel cell according to the tenth aspect of the invention, wherein the mixture contains 5 to 30% by weight of the fine particles and 5 to 30% by weight of the coarse particles. Thus, the electrical efficiency of the cell can be increased.
A twelfth aspect of the invention is a material for a base tube for a solid electrolyte fuel cell, the solid electrolyte fuel cell being produced by laminating a film of a fuel electrode, a film of an electrolyte, and a film of an air electrode in this order on a surface of the base tube, the material for the base tube comprising a mixture of a raw material for the base tube, and coarse particles, the raw material being calcia-stabilized zirconia (CSZ) having a mean particle diameter of 0.5 to 2 xcexcm, and the coarse particles having particle diameters of 5 xcexcm or more and being selected from one or more of NiO, CoO, FeO, Fe2O3, CaTiO3, SrTiO3, and BaTiO3. Thus, the electrical efficiency of the cell can be increased.
A thirteenth aspect of the invention is the base tube for a fuel cell according to the twelfth aspect of the invention, wherein the mixture contains 10 to 40% by weight of the coarse particles. Thus, the electrical efficiency of the cell can be -increased.
A fourteenth aspect of the invention is a material for a base tube for a solid electrolyte fuel cell, the solid electrolyte fuel cell being produced by laminating a film of a fuel electrode, a film of an electrolyte, and a film of an air electrode in this order on a surface of the base tube, the material for the base tube comprising a mixture of calcia-stabilized zirconia (CSZ) having a mean particle diameter of 0.5 to 2 xcexcm, 5 to 30% by weight, based on the CSZ, of fine particles having a mean particle diameter of 0.5 to 3 xcexcm, the fine particles being one or more of NiO, CoO and Fe2O3, and 5 to 30% by weight, based on the CSZ, of coarse particles having a mean particle diameter of 5 xcexcm or more, the coarse particles being one or more of NiO, CoO, Fe2O3 and CaO-stabilized ZrO2, whereby the mixture shrinks nonuniformly when sintered to increase the porosity of the base tube. Thus, the electrical efficiency of the cell can be increased.
A fifteenth aspect of the invention is a material for a base tube for a solid electrolyte fuel cell, the solid electrolyte fuel cell being produced by laminating a film of a fuel electrode, a film of an electrolyte, and a film of an air electrode in this order on a surface of the base tube, the material for the base tube comprising a mixture of calcia-stabilized zirconia (CSZ) having a mean particle diameter of 0.5 to 2 xcexcm, 5 to 30% by weight, based on the CSZ, of one or more of CaTiO3, SrTiO3, BaTiO3, and CaO-stabilized ZrO2 having a mean particle diameter of 0.5 xcexcm or more, and 5 to 30% by weight, based on the CSZ, of one or more of NiO, CoO, Fe2O3 having a mean particle diameter of 5 xcexcm or more, whereby the mixture shrinks nonuniformly when sintered to increase the porosity of the base tube. Thus, the electrical efficiency of the cell can be increased.